A very easy way would be to just register for the PageRemoved
event and if there are no other pages just close the form.
sender, Telerik.WinControls.UI.RadPageViewEventArgs e)
(radPageView1.Pages.Count == 0)
For more help and info on the PageView please take a look at this help article
Hope this helps, if you have any other questions or comments, please let me know,
Telerik WinForms MVP